Studies investigating the mechanisms of disease induction in susceptible animals often provide insight into how disease is initiated. Similarly, studies on how disease is prevented in resistant strains can also provide information for understanding the disease processes. The objective of this proposal is to use genetic and immunochemical approaches to probe some of the factors that confer resistance to the induction of experimental autoimmune encephalomyelitis (EAE) in mice. By adoptively transferring encephalitogenic cells between susceptible (SJL) and resistant (B10.S) mouse strains, the roles of antigen priming and of the cerebral endothelium in disease resistance are evaluated (specific aim 1). These experiments are aided by the novel use of Thy-1 congenic strains that allows rapid identification of donor versus host T cells in sections of CNS tissues. In specific aim 2, the question of whether expression of MHC antigens on cerebral endothelium is required for passage of encephalitogenic cells into the CNS is investigated. This is achieved by transferring encephalitogenic cells from one susceptible donor (SJL) into another allogeneic susceptible host (PL). Since expression of MHC antigens, if any, by the host endothelium will not be compatible with the donor T cells, any development of disease will indicate that recognition of MHC antigens on endothelial cells by encephalitogenic cells is not essential. In specific aim 3, fresh cerebral endothelial cells are established in vitro and the same lymphocyte-endothelial cell combinations as in specific aims 1 and 2 are used to examine the passage of lymphocytes through monolayers of endothelial cells. Results will be correlated with the in vivo observations. In specific aim 4, the role of host T cells in the generation of EAE in the two-step transfer-challenge protocol is investigated. This protocol successfully induces EAE in resistant strains and results from these experiments will provide insights into how EAE resistance in these mice is overcome. Finally, in specific aim 5, biochemical techniques will be used to map the myelin basic protein T cell epitopes stimulatory to the resistant B10.S mice using the transfer- challenge protocol. These epitopes will be compared to those recognized by the susceptible SJL cells as both strains share the same MHC haplotypes. The results obtained in this project, together with those from Project 1, should provide a comprehensive understanding of the resistant mechanism, especially the interactions between lymphocytes and the cerebral endothelium, in the development of EAE. This information will aid the design of therapeutic approaches to treat this autoimmune disease.